JP2005522890A - Reduction of transition in nonpolar gallium nitride thin films. - Google Patents

Abstract

The present invention relates to semiconductor materials, methods, and devices, and more specifically to transition reduction in thin nonpolar gallium nitride (GaN) layers. The present invention reduces the threading transition density in a-GaN by lateral overgrowth of planar heteroepitaxial “seed” layers. The lateral overgrowth technique requires a processing step between two MOCVD growths (the first heteroepitaxial growth and the regrowth that constitutes the lateral overgrowth). First, a thin patterned dielectric mask is applied to the seed layer.

Description

(Citation of related application)
This application is filed under 35 USC 119 (e) and is assigned to the same co-pending US Provisional Patent Application No. 60 / 372,909 (name of invention "NON-POLAR"). GALLIUM NITRIDE BASSED THIN FILMS AND HETEROSTRUCTURE MATERIALS ”, filing on April 15, 2002, Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal MarS. Claims the benefit of document number 30794.95-US-P1). This application is incorporated herein by reference.

This application relates to the following co-pending, commonly assigned US patent applications:
Application number ---------------------- NON-POLAR (AL, B, IN, GA) N QUANTUM WELL AND HEASTER STRUCTURE MATERIALS AND DEVICES, filed the same day as this application, Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal Margarith, James S. Speck, Shuji Nakamura and Umesh K. Misra, Attorney Document No. 30794.101-US-U1); and Application No.-/ ---, ----, title of invention "NON-POLAR A-PLANE GALLIUM NITRATION THIN FILM GROWN BY METALORGANIC CHAPICAL VAPOR" Filed on the same day as this application, Michael D. Craven and James S. Speck, agent document number 30794.100-US-U1);
Both of these applications are hereby incorporated by reference.

(1. Field of the Invention)
The present invention relates to semiconductor materials, methods, and devices, and more specifically to transition reduction in thin nonpolar gallium nitride (GaN) layers (2. Description of Related Art).
(Note: This application refers to a number of different patents, applications and / or publications as indicated throughout this specification by one or more reference numbers. These reference numbers for these different publications. An ordered list according to can be found in the section entitled “References” below, each of which is incorporated herein by reference).

  Current nitride-based devices use heterostructures grown along the polar [0001] c direction, resulting in the formation of a strong electrostatic field parallel to the growth direction. See references 1-7. A “built-in” electrostatic field is caused by a constant sheet charge associated with polarization discontinuities at surfaces and interfaces in c-plane (0001) nitride structures.

  These polarization-inducing electric fields affect the performance of current state-of-the-art optoelectronic nitride devices and electron nitride devices. For example, polarization fields spatially separate electron and hole wave functions in quantum well (QW) structures, thereby recombining carriers in QW-based devices (eg, laser diodes and light emitting diodes (LEDs)). Reduce efficiency. Furthermore, the polarization field induces a large movable sheet charge density in transistor structures using nitride heterostructures. A discontinuity in total polarization results in the formation of a constant sheet charge at the corresponding interface or surface.

  Epitaxial growth of nonpolar wurtz nitride semiconductor films offers a promising means to eliminate the effects of polarization-induced electric fields in nitride quantum structures. In the above related application, non-polar

ａ平面ＧａＮ膜（本明細書中で、ａ−ＧａＮと呼ばれる）は、金属有機化学蒸着（ＭＯＣＶＤ）によって、

An a-plane GaN film (referred to herein as a-GaN) is formed by metal organic chemical vapor deposition (MOCVD)

ｒ平面サファイア基板上で成長された。参考文献１３を参照のこと。しかし、これらの膜に存在するスレッディング転移密度は、約２．６×１０^１０ｃｍ^−２であると決定されている。

Grown on r-plane sapphire substrate. See reference 13. However, the threading transition density present in these films has been determined to be about 2.6 × 10 ¹⁰ cm ⁻² .

  In order to fully understand the advantages of non-polar nitride layers, it is necessary to improve the quality of the epitaxial film, and in particular to reduce the transition density. In particular, improving the crystal quality of these films is essential for the realization of high performance nitride devices that operate without polarization-induced electric fields.

  Various techniques have been shown, but the reduction of transition has been extensively studied in laterally overgrown polar GaN films. See references 8-11. Low dislocation density substrates obtained by various lateral overgrowth techniques directly bear the outstanding performance of nitride-based optoelectronics, most notably long-lived continuous wave InGaN laser diodes. See reference 12.

  Lateral overgrowth techniques are well known in the prior art. For example, lateral overgrowth techniques have been thoroughly studied for reducing transitions in polar c-plane (0001) GaN films. Specific overgrowth techniques include lateral epitaxial overgrowth (LEO) (also known as epitaxial lateral overgrowth (ELO or ELOG)), and PENDEO® epitaxy. Regardless of the difference between these processes, the reduction of transfer is achieved by common mechanisms, mainly mask blocking and transfer curvature. See references 11 and 19.

  However, the present invention is a novel application of these methods for GaN films. Specifically, the present invention describes a LEO method that uses an a-GaN seed layer, which achieves threading transition reduction. Low transition density a-GaN can be used as a buffer layer for (Al, B, In, Ga) N based devices that do not contain high performance polarization inductive fields.

(Summary of the Invention)
Nonpolar

ａ−平面ＧａＮ薄膜の横方向エピタキシャル過剰成長は、ＧａＮ膜におけるスレッディング転移を低減する。第１に、薄いパターン化誘電性マスクが、シード層に適用される。第２に、選択的エピタキシャル再成長が実施されて、パターン化マスクを基礎として横方向過剰成長ベースが達成される。再成長の際、ＧａＮ膜は、最初に、誘電性マスク中の開口部を通って垂直方向に成長し、その後、この垂直成長方向に対して垂直の方向でこのマスクを横方向に過剰成長させる。スレッディング転移は、（１）成長中の膜に向かう垂直方向の転移の伝達をブロックするマスク、および（２）垂直から横方向への成長の移行による転移の湾曲によって、過剰成長領域において低減される。

Lateral epitaxial overgrowth of a-plane GaN thin films reduces threading transitions in GaN films. First, a thin patterned dielectric mask is applied to the seed layer. Second, selective epitaxial regrowth is performed to achieve a lateral overgrowth base on the patterned mask. During regrowth, the GaN film is first grown vertically through the openings in the dielectric mask and then overgrown the mask laterally in a direction perpendicular to the vertical growth direction. . Threading transitions are reduced in overgrowth regions by (1) masks that block the transfer of vertical transitions to the growing film, and (2) transition curvature due to vertical to lateral growth transitions. .

  Reference is now made to the drawings. In the drawings, like reference numerals generally indicate corresponding parts.

(Detailed description of the invention)
In the following description of the preferred embodiments, reference is made to the accompanying drawings. The drawings form part of the present specification and by way of example specific embodiments in which the invention may be practiced may be described. It should be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

(Outline)
The present invention reduces the threading transition density in a-GaN by lateral overgrowth of planar heteroepitaxial “seed” layers. The lateral overgrowth technique requires a processing step between two MOCVD growths (first heteroepitaxial growth and regrowth that constitutes lateral overgrowth). First, a thin patterned dielectric mask is applied to the seed layer. During regrowth, GaN first grows perpendicularly through the openings in the dielectric mask and then overgrows the mask laterally in a direction perpendicular to the vertical growth direction. . With an appropriate mask and regrowth conditions, the transition density is reduced in the lateral overgrowth region compared to the region grown vertically through the openings in the mask. The transition is reduced in the overgrowth region by (1) a mask that blocks the transmission of the vertical transition towards the growing film, and (2) the curvature of the transition due to the growth transition from vertical to lateral.

(Process process)
FIG. 1 is a flow chart illustrating steps for reducing threading transition density in a-GaN due to lateral overgrowth of planar heteroepitaxial “seed” layers, in accordance with a preferred embodiment of the present invention.

  Block 100 is a co-pending U.S. Provisional Patent Application No. 60 / 372,909 (invention name "NON-POLAR GALLIUM NITRIDE BASIC THIN FILMS AND HETEROSTUCTURE MATERIALS", filed April 15, 2002. , Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal Margarith, James S. Speck, Shuji Nakamura, and Umesh K. Mishara, attorney document number 30794. US patent application number assigned to the same person ------, ---, title of invention "NON-POLAR A-PLANE GALL" “IUM NITRIDE THIN FILMS GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION”, filed on the same day as this application, Michael D. Craven and James S. Speck, attorney document number 30794.100-US-U1) (both of these applications are incorporated herein by reference) by MOCVD,

ｒ平面サファイア基板上における、非極性

Nonpolarity on r-plane sapphire substrate

ａ平面ＧａＮ薄膜の成長を表す。ヘテロエピタキシャル成長した非極性

It represents the growth of a planar GaN thin film. Heteroepitaxial nonpolarity

ａ平面ＧａＮ薄膜は、本発明の横方向過剰成長のための「シード層」を含む。

The a-plane GaN thin film includes the “seed layer” for lateral overgrowth of the present invention.

  Block 102 is non-polar

ａ平面ＧａＮフィルム上に、プラズマ増強化学的蒸着堆積（ＰＥＣＶＤ）を介して誘電性再成長マスク（ｄｉｅｌｅｃｔｒｉｃ ｒｅｇｒｏｗｔｈ ｍａｓｋ）を堆積させる工程を示す。好ましい実施形態において、このマスクは、２００ナノメートル（ｎｍ）のＳｉＯ_２から構成されるが、これに限定されない。

FIG. 4 shows a process of depositing a dielectric regrowth mask on a planar GaN film via plasma enhanced chemical vapor deposition (PECVD). FIG. In a preferred embodiment, the mask is constituted of SiO ₂ of 200 nanometers (nm), but is not limited thereto.

Block 104 represents the step of patterning the deposited mask, where this pattern is transferred to SiO ₂ using conventional photolithographic techniques and wet etching with buffered hydrofluoric acid. . Preferably, the deposited mask is patterned with long, narrow stripe openings oriented in various crystallographic directions.

  After patterning the mask, block 106 represents the step of cleaning the sample using a solvent.

  Block 108 represents the step of performing selective epitaxial regrowth to achieve lateral overgrowth based on the patterned mask, where the gallium nitride is initially perpendicular through the openings in the mask. The mask is then overgrown laterally in a direction perpendicular to the vertical growth direction. The dislocation density is reduced in vertically overgrown regions compared to regions that grow vertically through openings in the mask. In addition, dislocations are reduced in the overgrowth region by masks that block the dislocation spread in the vertical direction to the growth film and by bending of the dislocations due to the growth transition from vertical to lateral direction.

  Preferably, block 108 is the same reactor conditions as those used for heteroepitaxial growth on the sapphire substrate (ie, about 1100 ° C. growth temperature, about 1300 V / III rate, and about 0.1 atmosphere (atm) growth pressure. ), But modified conditions may be used.

  Block 110 represents the resulting lateral overgrowth, where the lateral overgrowth includes laterally overgrown GaN with stripes as determined by the underlying mask pattern. Overgrowth stripe morphology depends on the crystallographic orientation of the mask stripe. For example,

に対して整列されたストライプは、矩形の断面を有し、そして、過剰成長領域においてかなりの転位の減少を示す。

The stripes aligned with respect to have a rectangular cross-section and show significant dislocation reduction in the overgrown region.

  Possible devices that can be fabricated using this method include laser diodes (LDs), light emitting diodes (LEDs), resonant cavity LEDs (RC-LEDs), vertical cavity surface emitting lasers (VCSELs), high electron mobility transistors (HEMT), heterojunction bipolar transistor (HBT), heterojunction field effect transistor (HFET), and UV and near UV photodetectors.

(Experimental result)
Lateral epitaxial overgrowth is nonpolar

ａ平面ＧａＮフィルムの螺旋転位（ｔｈｒｅａｄｉｎｇ ｄｉｓｌｏｃａｔｉｏｎ）密度を首尾良く減少させたという実験結果が、見出された。この節では、形態学および欠損減少の結晶学的ストライプ配向に対する依存性を報告する。

Experimental results have been found that have successfully reduced the threading dislocation density of a-plane GaN films. In this section, we report the dependence of morphology and defect reduction on crystallographic stripe orientation.

  [0001] and

に沿って整列されたストライプは、最も好ましいａ平面ＧａＮ ＬＥＯストライプ配向であり、良く整えられた（ｗｅｌｌ−ｂｅｈａｖｅｄ）対称的な形態学を保有する。マスクブロッキングを介する螺旋転位減少を、最適な矩形断面を有する

The stripes aligned along are the most preferred a-plane GaN LEO stripe orientation and possess a well-behaved symmetrical morphology. Spiral dislocation reduction through mask blocking, with optimal rectangular cross section

ストライプに対する透過電子顕微鏡（ＴＥＭ）によって観察した。カソードルミネセンス（ＣＬ）研究は、ウィンドウ領域と比較して過剰成長領域に対して増加した発光を示した。これらのストライプの横方向過剰成長の程度は、垂直ｃ平面サイドウォールの反体の極性に起因して非対称的であった。逆に、螺旋転位は、同時に存在する曲がったかつ垂直な

Observation was performed by transmission electron microscope (TEM) on the stripe. Cathodoluminescence (CL) studies showed increased luminescence for the overgrown region compared to the window region. The extent of lateral overgrowth of these stripes was asymmetric due to the polarity of the vertical c-plane sidewall reciprocal. Conversely, screw dislocations are curved and vertical that exist simultaneously

面を保有する［０００１］ストライプの対称的な過剰成長領域に広がった。

It spreads over a symmetrical overgrowth region of [0001] stripes holding the plane.

Stripe morphology was observed using a JEOL 6300 ^TM field emission scanning electron microscope (FE-SEM) operating at 5 kV. Lateral overgrowth microstructures were studied in cross-section using a JEOL 2000FX ^™ transmission electron microscope (FE-SEM) operating at 200 kV. Cathodoluminescence (CL) images were obtained using a Gatan MonoCL ^™ attached to a JEOL 6300 ^™ FE-SEM at room temperature and provided a spatial map of luminescence from lateral overgrowth stripes.

As shown for laterally overgrown c-plane GaN, the crystallographic orientation of the mask stripe opening thus describes the plane that forms the lateral overgrowth feature. See reference 14. To investigate the overgrown a-GaN orientation dependence in the horizontal direction, and patterned by any of the array of the rectangular mask opening to form the a SiO ₂ mask "wagon wheel" design (window). The windows that make up the wagon wheel pattern were oriented with 5 μm width and 5 ° spacing so that the range of crystallographic mask orientation could be analyzed by performing a single MOCVD growth. This experimental design is similar to the design used for the initial investigation of c-plane GaN overgrown laterally from the linear mask opening. See references 14 and 15.

  FIG. 2 is a top view manipulated electron microscope (SEM) image montage showing half of the a-GaN LEO wagon wheel pattern. This angle is included to facilitate reference to a wagon wheel pattern where 0 ° corresponds to the GaN c-axis [0001]. The reduced symmetry of the a-GaN surface (relative to the c-GaN surface) is evident in the stripe orientation dependence shown in FIG. This figure is a 180 ° view of a single wagon wheel pattern. Mainly, this top view SEM image shows that lateral overgrowth has occurred for all possible stripe orientations. When examined closer, the three stripe orientations have a uniform morphology without the faceted sidewalls: parallel to [0001], 45 ° away from the GaN c-axis And perpendicular to the GaN c-axis (

方向に対して平行）。ｃ−軸から４５°離れて配向したストライプは、

Parallel to the direction). A stripe oriented 45 ° away from the c-axis is

ストライプとして指標とされる。なぜなら、この結晶学的方向は、ｃ−軸との角度を４６．８°にするためである。図２は、［０００１］から

It is used as an index as a stripe. This is because this crystallographic direction makes the angle with the c-axis 46.8 °. 2 starts from [0001]

まで変化したストライプ配向のように、ストライプ幅が、最大幅がｃ−軸から７０°離れて整列したストライプに達するまで増加したことを示す。この最大に達した後に、ストライプ幅は、

As the stripe orientation has changed to, the stripe width has increased until the maximum width reaches a stripe aligned 70 ° away from the c-axis. After reaching this maximum, the stripe width is

に達するまで減少した。特定の結晶学的指標付けは、ｃ−ＧａＮと比較して、このフィルム／基板系の減少した対称性に起因して、この説明全体を通して一致して使用されることに留意のこと。

Decrease until reached. Note that specific crystallographic indexing is used consistently throughout this description due to the reduced symmetry of this film / substrate system compared to c-GaN.

  In order to clearly observe the effect of stripe orientation on a-GaN LEO morphology, further perspective views are needed. 3 (a), (b) and (c) are [0001],

に対して平行に配向した３つのストライプの曲がった図による一連のＳＥＭ画像である。ここで、これらの画像は、図２における０°、４５°、および９０°の配向標識に対応する（そして、５５μｍに相当するスケールバーを有する）。

FIG. 3 is a series of SEM images with a bent view of three stripes oriented parallel to the. Here, these images correspond to the orientation labels of 0 °, 45 °, and 90 ° in FIG. 2 (and have scale bars corresponding to 55 μm).

  For the growth conditions used, [0001] and

のストライプは、曲がったサイドウォールおよび垂直なサイドウォールの種々の組み合わせを有した。特に、対称的な形態学を［０００１］ストライプについて観察し、一方、

The stripes had various combinations of curved and vertical sidewalls. In particular, symmetric morphology is observed for [0001] stripes, while

ストライプは、１つの微小切子面垂直

The stripe is perpendicular to one microfacet

サイドウォールおよび１つの曲がった

Side wall and one bent

サイドウォールを有する非対称的な形態学を有した。［０００１］ストライプは、

Has an asymmetric morphology with sidewalls. [0001] The stripe

平面の同じ結晶学的ファミリーからの同時に存在する垂直面および曲がった面を有した。逆に、

It had vertical and curved surfaces that existed simultaneously from the same crystallographic family of planes. vice versa,

ストライプは、垂直な（０００１）基礎平面サイドウォールを有する矩形断面を有した。全体的に、［０００１］配向および

The stripe had a rectangular cross section with a vertical (0001) foundation plane sidewall. Overall, the [0001] orientation and

ストライプ配向は、均一で対称的な形態学を生じた。

The stripe orientation resulted in a uniform and symmetric morphology.

  4 (a), (b) and (c)

ストライプの断面ＴＥＭ画像であり、ここで、図４（ａ）は、非対称的な過剰成長領域における螺旋転位減少を示す。図４（ａ）において破線四角によって規定されるマスク縁部領域の拡大図が、図４（ｂ）

FIG. 4A is a cross-sectional TEM image of a stripe, where FIG. An enlarged view of the mask edge region defined by the broken-line square in FIG. 4A is shown in FIG.

ストライプおよび図４（ｃ）

Stripe and Figure 4 (c)

ストライプについて示される。この転位線は、ウィンドウ領域から［０００１］に沿って整列したストライプに対する過剰成長領域へ屈曲し、この間、転位屈曲は、

Shown for stripes. This dislocation line bends from the window region to the overgrowth region for stripes aligned along [0001], during which the dislocation bend is

ストライプについては観察されない。図４（ａ）、（ｂ）および（ｃ）は、種々の回折条件での明瞭場画像である：図４（ａ）ｇ＝

No stripes are observed. 4 (a), 4 (b) and 4 (c) are clear field images under various diffraction conditions: FIG. 4 (a) g =

、図４（ｂ）ｇ＝０００６、および図４（ｃ）ｇ＝

4 (b) g = 0006 and FIG. 4 (c) g =

。画像化されたストライプは、平行なストライプパターン（および、ワゴンホイールパターンではない）からのもであるが、類似の形態学をマスクストライプパターンに関わらず観察した。

. The imaged stripes were from a parallel stripe pattern (and not a wagon wheel pattern), but similar morphology was observed regardless of the mask stripe pattern.

  The decrease in threading dislocation (TD), as shown in the cross-sectional TEM image in FIG.

に沿って整列したＬＥＯストライプについて観察された。転移が、図４（ｂ）に示されるよに、横方向の過剰成長の方向へ屈曲することが観察されないので、マスクブロッキングは、主な転移減少機構である。

Was observed for LEO stripes aligned along. Mask blocking is the main dislocation reduction mechanism because the transition is not observed to bend in the direction of lateral overgrowth, as shown in FIG. 4 (b).

ストライプと異なり、図４（ｃ）は、転移が［０００１］に沿って整列するストライプの過剰成長領域へと広がったことを示す。この転移屈曲の正確な起源は、未だ未知であるが、［０００１］ストライプ方向について曲げられた面の安定性は、重要な役割を果す。

Unlike the stripe, FIG. 4 (c) shows that the transition has spread to the overgrowth region of the stripe aligned along [0001]. The exact origin of this transition bend is not yet known, but the stability of the surface bent in the [0001] stripe direction plays an important role.

  In addition to the decrease in TD, FIG.

ストライプに対する横方向過剰成長速度における非対称を明らかにする。極性のｃ平面サイドウォールの存在は、この非対称を説明する。ストライプ方向に対して垂直な極性軸で、１つのサイドウォールは、＋ｃ平面またはＧａ−面であり、一方、反対のサイドウォールは、−ｃ平面またはＮ−面である。予期されるように、Ｇａ−面サイドウォールは、成長条件に依存して約１０倍Ｎ−面サイドウォールよりも速く成長する。ｒサファイア上のａ−ＧａＮの極性は、収束性ビーム電子回折測定を使用して以前に測定されたことが記載される。参考文献１３を参照のこと。極性は、

Reveal asymmetry in lateral overgrowth rate for stripes. The presence of polar c-plane sidewalls explains this asymmetry. With a polar axis perpendicular to the stripe direction, one sidewall is the + c plane or Ga-plane, while the opposite sidewall is the -c plane or N-plane. As expected, Ga-plane sidewalls grow about 10 times faster than N-plane sidewalls depending on growth conditions. It is described that the polarity of a-GaN on r-sapphire was previously measured using convergent beam electron diffraction measurements. See reference 13. Polarity is

ストライプの横方向過剰成長にこのような有意な効果を有するので、図２および３において観察される非対称な形態学が、構造の低い対称性に関連し得る。

Since having such a significant effect on the lateral overgrowth of the stripes, the asymmetric morphology observed in FIGS. 2 and 3 may be related to the low symmetry of the structure.

  Further evidence of lateral overgrowth asymmetry for polar GaN is [0001],

および

and

のＬＥＯストライプの平面多色ＣＬ画像によって提供された。図５（ａ）、（ｂ）および（ｃ）は、［０００１］、

Provided by a planar multicolor CL image of the LEO stripes. 5 (a), (b) and (c) are [0001],

および

and

に対して平行に配向されたストライプの平面多色ＣＬ画像であり、一方、図５（ｄ）は、図５（ａ）、（ｂ）および（ｃ）に対して結晶学的方向を図示する。ＣＬ画像は、図３（ａ）、（ｂ）および（ｃ）におけるＳＥＭによって画像化されたストライプに直接的に対応して、図５（ａ）〜（ｃ）に示した（そして、５５μｍを示すスケールバーを有する）。各ストライプ方向内での斑点領域は、ＳｉＯ_２マスクにおけるウィンドウを規定し、ＴＤは、ＬＥＯストライプの上面に妨げられずに延びる。このＣＬ特徴は、極性ＧａＮ ＬＥＯストライプに観察された。参考文献１６〜１８を参照のこと。斑点領域は、［０００１］ストライプの全体の幅を横切って伸び、これは、このストライプの方向に対して横方向過剰成長領域への転移屈曲のＴＥＭ観察に対応する。図５（ａ）〜（ｃ）に示される［０００１］ストライプは、わずかな横方向過剰成長を有するにもかかわらず、同様の条件下で成長した幅広いストライプのＣＬ測定は、図４（ｃ）において観察される転移屈曲を確立した。

FIG. 5 (d) illustrates the crystallographic directions for FIGS. 5 (a), (b) and (c). . CL images are shown in FIGS. 5 (a)-(c), directly corresponding to the stripes imaged by SEM in FIGS. 3 (a), (b) and (c) (and 55 μm). With scale bar shown). The speckled area within each stripe direction defines a window in the SiO ₂ mask and the TD extends unimpeded by the top surface of the LEO stripe. This CL feature was observed in polar GaN LEO stripes. See references 16-18. The speckled region extends across the entire width of the [0001] stripe, which corresponds to a TEM observation of the transition bend to the lateral overgrowth region with respect to the direction of the stripe. Although the [0001] stripes shown in FIGS. 5 (a)-(c) have slight lateral overgrowth, CL measurements of a wide stripe grown under similar conditions are shown in FIG. 4 (c). Established the metastasis bend observed in.

ストライプの過剰成長領域からの均一なルミネセンスは、これらの領域が相対的にＴＤを含まないことを確認する。

The uniform luminescence from the overgrown areas of the stripe confirms that these areas are relatively free of TD.

ストライプの横方向過剰成長速度に対する極性の効果がまた、明らかに観察される。

The effect of polarity on the lateral overgrowth rate of the stripe is also clearly observed.

  In summary, nonpolar

ａ平面ＧａＮフィルムのＬＥＯは、証明され、そしてＴＤ密度の減少が達成された。低対称性のａ−ＧａＮ表面は、結晶学的ストライプ整列に依存したＬＥＯストライプ形態学を示した。２つの主な方向（［０００１］および

The a-plane GaN film LEO was proven and a reduction in TD density was achieved. The low symmetric a-GaN surface showed LEO stripe morphology depending on crystallographic stripe alignment. Two main directions ([0001] and

）は、均一な対称性ストライプ形態学を有することが観察され；

) Is observed to have a uniform symmetric stripe morphology;

ストライプは、垂直なサイドウォールを有し、一方、［０００１］ストライプは、同時に存在する垂直なサイドウォールおよび曲がったサイドウォールを有した。転移減少は、

The stripes had vertical sidewalls, while the [0001] stripes had coexisting vertical and bent sidewalls. Metastasis reduction is

ストライプ中で達成され、一方、転移は、［０００１］ストライプの横方向過剰成長領域へと広がった。［０００１］と

While achieved in the stripes, the transition spread into the lateral overgrowth region of the [0001] stripes. [0001] and

との間の方向（非対称性のストライプ形態学）が、観察された。非極性の横方向成長方向を有する［０００１］ストライプを除いて、全てのストライプは、非対称性の横方向成長速度を示した。継続中の研究は、非極性ＧａＮ ＬＥＯの独特な構造的特性の調査を続ける。

A direction between (asymmetric stripe morphology) was observed. All stripes exhibited asymmetric lateral growth rates, with the exception of [0001] stripes having a non-polar lateral growth direction. Ongoing research continues to explore the unique structural properties of nonpolar GaN LEO.

(References)
The following references are hereby incorporated by reference:

（結論）
これは、発明の好ましい実施形態の説明を結論付ける。以下は、本発明を達成するための、いくつかの代替の実施形態を記載する。

(Conclusion)
This concludes the description of the preferred embodiment of the invention. The following describes some alternative embodiments for accomplishing the present invention.

  Critical aspects of lateral overgrowth technology are dielectric mask specificity and MOCVD regrowth conditions. A variety of dielectric materials, deposition techniques and patterning methods can be used to assemble a mask that is effective for lateral overgrowth. Furthermore, altering the direction, design and dimensions of the mask pattern ultimately determines the characteristics of subsequent lateral overgrowth. Sufficient control of lateral overgrowth is necessary to achieve transfer reduction and complete overgrowth of the mask, so that the planar film is reformed. Specific details of lateral overgrowth (including lateral to vertical growth rate ratio and sidewall surface stability) are controlled by MOCVD regrowth conditions. MOCVD growth conditions are reactor dependent and can vary between specific reactor designs. Fundamental variations in conditions such as growth temperature, growth pressure, V / III ratio, precursor flow, and feed are possible modifications of the invention.

  Furthermore, metastasis reduction can also be achieved using alternative overgrowth methods. For example, cantilever epitaxy, double lateral epitaxial overgrowth (Double LEO) and SiN nanomasking techniques can be used as an alternative to lateral epitaxial overgrowth.

  Furthermore, although non-polar a-plane GaN thin films are described herein, the same technique is applicable to non-polar m-plane GaN thin films. Furthermore, non-polar InN thin films, AlN thin films, and AlInGaN thin films can be used instead of GaN thin films.

  Finally, substrates other than sapphire substrates can be used for nonpolar GaN growth. These substrates include silicon carbide, gallium nitride, silicon, zinc oxide, boron nitride, lithium aluminate, lithium niobate, germanium, aluminum nitride, and lithium gallate.

  In summary, the present invention is non-polar, resulting in reduced helical transitions.

ａ平面ＧａＮシード層の横方向エピタキシャル過剰成長を記載する。第１に、薄いパターン化した誘電性マスクが、シード層に適用される。第２に、選択的なエピタキシャル再成長が行われ、パターン化マスクの横方向過剰成長が達成される。再成長の際に、ＧａＮフィルムは、垂直な成長方向に対して垂直な方向においてマスクを横方向過剰成長する前に、最初に誘電性マスクの開口部を通って垂直に成長する。螺旋転移は、（１）成長フィルムに対して垂直な転移の広がりをブロックするマスクおよび（２）垂直から横方向までの成長の移行による転移の屈曲によって過剰成長領域を減少する。

A lateral epitaxial overgrowth of the a-plane GaN seed layer is described. First, a thin patterned dielectric mask is applied to the seed layer. Second, selective epitaxial regrowth is performed to achieve lateral overgrowth of the patterned mask. During regrowth, the GaN film first grows vertically through the openings in the dielectric mask before lateral overgrowth of the mask in a direction perpendicular to the vertical growth direction. The spiral transition reduces the overgrowth region by (1) a mask that blocks the spread of the transition perpendicular to the growth film and (2) the bending of the transition due to the growth transition from vertical to lateral.

  The foregoing description of one or more embodiments of the invention has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in view of the above teachings. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

に対して平行に配向された３つのストライプの傾けられた図を含む一連のＳＥＭ画像である。
図４（ａ）、（ｂ）および（ｃ）は、

ストライプの断面ＴＥＭ画像である。
図５（ａ）、（ｂ）および（ｃ）は、

に対して平行に配向されたストライプの平面多色ＣＬ画像であり、一方、図５（ｄ）は、図５（ａ）、（ｂ）および（ｃ）の結晶学的配向を示す。 FIG. 1 is a flow chart illustrating steps for reducing threading transition density in a-GaN due to lateral overgrowth of planar heteroepitaxial “seed” layers, in accordance with a preferred embodiment of the present invention. FIG. 2 is a scanning electron microscope (SEM) image photograph showing half of the a-GaN LEO wagon wheel pattern. 3 (a), (b) and (c) are respectively shown in FIG.

Is a series of SEM images including a tilted view of three stripes oriented parallel to.
4 (a), (b) and (c)

It is a cross-sectional TEM image of a stripe.
5 (a), (b) and (c)

FIG. 5 (d) shows the crystallographic orientation of FIGS. 5 (a), (b) and (c).

Claims (12)

A method for reducing the helical transition density in a nonpolar a-plane gallium nitride thin film, comprising the following steps: (a) depositing a dielectric regrowth mask on the nonpolar a-plane gallium nitride thin film;
(B) patterning the deposited mask; and (c) performing selective regrowth to achieve overgrowth based on the patterned mask;
Including the method. The method of claim 1, wherein the non-polar a-plane gallium nitride thin film includes a seed layer. The method of claim 1, wherein the depositing comprises depositing a dielectric regrowth mask on the non-polar a-plane gallium nitride thin film by plasma enhanced chemical vapor deposition (PECVD). The method of claim 1, wherein the deposited mask is patterned with openings of long narrow stripes oriented in various crystallographic directions. The method of claim 1, wherein the overgrowth comprises laterally overgrown striped gallium nitride. The step of performing includes selective regrowth of the gallium nitride to achieve overgrowth based on a patterned mask, and the gallium nitride mask in a direction perpendicular to the vertical growth direction. The method of claim 1, wherein the first growth is vertical through the openings in the mask before lateral overgrowth therein. The method of claim 6, wherein the lateral overgrowth region includes a reduced dislocation density as compared to a region that grows vertically through an opening in the mask. 8. The method of claim 7, wherein the transition is reduced by a mask that blocks the spread of the vertical transition to the growth film. The method of claim 7, wherein the transition is reduced in overgrowth by bending of the transition through a transition from vertical growth to lateral growth. The method of claim 1, wherein the overgrowth is performed using lateral epitaxial overgrowth. The overgrowth is performed using a method selected from the group consisting of: cantilever epitaxy, double lateral epitaxial overgrowth (Double LEO) and SiN nanomasking. The method according to 1. A device made using the method of claim 1.

Images